Conceptual design of a building with columns and shear walls
1.Ans
For Arrangement (a)
Restraint of Floor shrinkage
- Observation: Full restraints at all corners
- Conclusion: Arrangement (a) will have higher restraint to shrinkage, thus lead to cracks in the floor.
The Lateral stiffness
- Observation: Comparatively Lower Lateral stiffness in both X and Y
Torsion with respect to vertical axis
- Observation: Corner Walls provide more resistance to twist
- Conclusion: Arrangement (a) will be best option with respect to Torsional resistance.
Vertical reinforcement for similar base capacity
- Observation: Walls are subjected to nominal flexural moment and heavy twisting moment
Static eccentricity
- Observation: Structurally symmetric
System's redundancy
- Observation: Uniform placement of lateral load supports in both the axes
- Conclusion: Arrangement (a) has more redundant
Foundation systems
- Observation: Due to 'L' shaped Walls, the geometry of foundation and its design will be critical
- Conclusion: Arrangement (a) is recommended to have peripheral box foundation
Architectural constraints
- Observation: Walls obstruct only comers.
- Conclusion: Architecturally speaking. Arrangement (a) is the preferred one.
For Arrangement (b)
Restraint of Floor shrinkage
- Observation: Corners are left free but restraints along the edge
- Conclusion: Arrangement (b) will have average restraint to shrinkage, thus average cracks
The Lateral stiffness
- Observation: Uniform and comparatively higher lateral stiffness in both X and Y
- Conclusion: Arrangement (b) will provide higher lateral stiffness for a pure seismic acceleration in X and Y directions
Torsion with respect to vertical axis
- Observation: Edge Walls provide good resistance to twist
Vertical reinforcement for similar base capacity
- Observation: Walls are subjected to nominal twisting moment
- Conclusion: Arrangement (b) will require the least
Static eccentricity
- Observation: Structurally symmetric
System's redundancy
- Observation: Uniform placement of lateral load supports in both the axes
- Conclusion: Arrangement (b) has more redundant
Foundation systems
- Observation: Walls are in line. Easy to fix the geometry and design of foundation
- Conclusion: Arrangement (b) shall be incorporated with isolated footings/strip footings
Architectural constraints
- Observation: Walls obstruct the faces of building.
- Conclusion: Architecturally speaking. Arrangement (b) is subjected to discussion
For Arrangement (c)
Restraint of Floor shrinkage
- Observation: Non-uniform restraints
- Conclusion: Arrangement (c) will not effectively restrain the shrinkage, so possibly less cracks
The Lateral stiffness
- Observation: Non uniform Lateral stiffness in both X and Y
Torsion with respect to vertical axis
- Observation: Irregular Walls provide very poor resistance to twist
- Conclusion: Arrangement (c) is the worst one
Vertical reinforcement for similar base capacity
- Observation: Walls are subjected to heavy flexural moment and twisting moment
- Conclusion: Arrangement (c) will require higher vertical reinforcement
Static eccentricity
- Observation: Un-symmetric
- Conclusion: Only Arrangement (c) will have static eccentricity and it is significant
System's redundancy
- Observation: Concentrated lateral load supports in both the axes
- Conclusion: Arrangement (c) has least redundant
Foundation systems
- Observation: Walls are in line & concentrated. Easy to fix the geometry of foundation but critical in design
- Conclusion: Arrangement (c) shall be incorporated with isolated footings/strip footings
Architectural constraints
- Observation: Vertical wall will not allow passage
- Conclusion: Architecturally speaking. Arrangement (c) will not be accepted both architecturally and commercially.
2.Ans
Issues in the given Framing plan:
- Indirect lateral load Transfer in X and Y directions - The beams are connecting to another beams which is ineffective during lateral load transfer.
- In such conditions, the primary beam is prone to shear failure.
Issues in the given Framing plan:
- Eccentricity- The longer the distance between center of mass and center of stiffness, the higher torsional moment of the building.
- As per the given plan eccentricity, the building is subjected to higher torsional moment (Torsional flexibility) in both X and Y directions.
Issues in the given Framing plan:
Strong beam Weak Column possibility
- The size of columns majorly mentioned as 25 cm x 25 cm.
- But all the beams have much deeper section (50cm).
- Inertia of beam is visually higher than column.
- If the column reinforcement is adequately greater than that of beams, we are okay and since we do not have the reinforcement detail, this is doubtful.
- It is recommended to have slight bigger sizes for column.
Alternate Scheme:
3.Ans
Observations in the given Framing plan:
- Floor plan - The floor plan of building is not either uniform or symmetric.
- So naturally any lateral load induced in the floor will not have 100% influence in same direction.
- Definitely a Special lateral load resisting system for these torsional moments should be accommodated.
- Random Internal columns - Since the internal columns are random, they are unable to transfer lateral loads efficiently and cannot achieve desirable building response.
- So, we have to assume and design those columns for only gravity loads.
- Floor to floor variations in Partition walls and Beams - Partition walls provide an important mass control in a building and beams play key role in shear transfer from floor to beam.
- All these elements are not in order. So heavy distortion and distribution of lateral loads will happen.
Suggestion on the Lateral load system & Its foundation:
- Heavy torsional forces should be controlled by respective lateral load system. So "Corner Shear walls" are suggested.
- The proportion of floor area is greater on the left side than the right side (Irregular quadrilateral). So Corner shear walls on the left side should be heavier than the right.
- Corner Shear walls shall preferably be supported over a box foundation. Shear walls should be connected by Link beams to transfer shear from one to the other.
- The internal columns shall be supported by isolated footings. Those isolated footings can be connected with Shear walls through Tie beams.
Proposed Schematic plan of Lateral load system:
Superstructure
Sub-structure